1. Field of the Invention
This invention relates to the interior coating of an elongate hollow member substantially vertically disposed or at least having a substantial vertical component of its longitudinal dimension. An example of such a member is a pipe or tubing disposed in a well in the earth in which event the coating material employed would be likely to be some protective coating or anticorrosive material. Such material is normally a liquid but is more or less viscous and is of a character which tends to cling to the walls of the pipe or tubing and form a slug therein. It is also important that the entire interior of the pipe or tubing be coated because any spots or streaks or other portions not coated are likely to be even more subject to corrosive influences than if the pipe as a whole were not coated.
Where the coating operation is to be carried on in a well which is producing gas on the like it is important that the production be not interrupted any longer than absolutely necessary. Hence it is important to minimize the time required for coating the pipe in the well as well as to insure its complete coating.
2. Description of the Prior Art
Various means have been employed for coating the inside of a pipe in a well with anticorrosive chemicals or with other substances found desirable in any particular case, but perhaps the most commonly used is the method whereby a body of liquid anticorrosive chemical estimated to be sufficient to coat the inside of the pipe in question is injected into the upper end thereof and allowed to fall by gravity to the lower end.
This method involves a number of non-desirable features:
1. The interior surface coverage is likely to be incomplete. In practice the rather viscous liquid tends to flow down one side of the pipe and adhere thereto as it flows instead of moving down as a complete plug or as a sheet of liquid completely covering the interior surface of the pipe.
2. The liquid flowing over the surface of the pipe may not completely wet the entire surface of the pipe but may, after flowing past, withdraw from the surface of the pipe leaving it uncoated in spots.
3. Particularly where the well is on an inclination to the vertical there is a strong tendency for the liquid to run down the lower side of the tubing or pipe and coat that side only, leaving the upper side of the interior of the pipe uncoated.
4. Contrary to what might be expected, the movement of chemical downwardly within a tubular member such as a well tubing is very slow as a rule. The chemical seems to be inclined to form a piston within the tubing and move downwardly at a pace of perhaps not more than 1,000 feet per hour, or a little over 16 feet a minute, requiring for deep wells from 12 to 24 hours for the chemical to move from top to bottom. This of course is highly undesirable in requiring an extremely long well shut down time.
No representation is made that the method above described is the only one employed for the purpose, but it is believed to be the most widely used and to be the most satisfactory prior to the present invention, as evidenced by its wide use.